1. Field of the Invention
The present invention relates to a visible light communication technology, and more particularly, to a visible light communication method and a transmitter/receiver for allowing a user to intuitively know a communication state, a transmission speed, or a transmission rate in visible light communication.
2. Description of the Related Art
Visible light is light having a wavelength in a range that is visible to the human eye among electromagnetic waves, in which the wavelength of the visible light is in the range of 380 to 780 nm. In the visible light, a change in property depending on the wavelength is displayed by colors and the wavelength becomes shorter from a red color to a purple color. Light having a wavelength longer than the red color is referred to as infrared rays and light having a wavelength shorter than the purple color is referred to as ultraviolet rays. Monochromic light emits specific wavelengths ranges for each color, for example, the red color emits between 700 to 610 nm, an orange color emits between 610 to 590 nm, a yellow color emits between 590 to 570, a green color emits between 570 to 500 nm, a blue color emits between 500 to 450 nm, and the purple color emits between 450 to 400. When the colors of the wavelengths are mixed, various colors are seen to the human eye.
Visible light wireless communication as a communication technology using a wavelength in the range of 380 to 780 nm is being standardized by the IEEE 802.15 WPAN (wireless personal area network) and in Korea, a visible light wireless communication task force of the Telecommunication Technology Association (TTA) is in operation.
The visible light communication enables wireless communication while utilizing a light emitting diode (LED)'s unique use such as lighting, etc. as it is. Further, since the visible light communication can be utilized even in an area under communication restrictions such as a hospital or an airplane, the visible light communication is expected to come into the spotlight as the next-generation ubiquitous technology.
In general, a visible communication transmitter/receiver includes a transmitting unit, a receiving unit, and a data transferring unit. The transmitting unit is constituted by light sources converting an electrical signal into a signal of a visible light band and a control unit controlling each light source. The receiving unit is constituted by a photo detector (PD) converting the signal of the visible light band into an electrical signal. The data transferring unit transfers data of an upper layer to be transmitted in each terminal to the transmitting unit and transfers data transferred from the receiving unit to the upper layer.
Environments using the visible communication transmitter and receiver may include an indoor lighting environment using an indoor lighting device, etc. and an outdoor signal lamp environment using a signal lamp, etc. In the visible light communication environment, when the visible light generated by the visible light communication transmitting unit is blocked due to obstacles regardless of an indoor environment or an outdoor environment, the visible light communication cannot be made between the transmitter and the receiver.
In the visible light communication, unlike a communication environment using a radio frequency (RF), the presence or not of obstacles has a significant influence on the communication environment. That is, the visible light communication is made under a line of sight (LOS) environment and unlike the RF communication environment, the location of the receiver may be shifted to a more appropriate location by user's intuitive judgment. Therefore, the visible light communication needs to allow a user to intuitively grasp a receiving angle of the photo detector and interference caused by another adjacent light source.
The related art has introduced a visible light communication apparatus that makes different light intensity in a case of transmitting only a pilot pattern because synchronization between transmission and reception is not made and light intensity when the synchronization is made to transmit data. According to the technology, whether or not transmission and receiving channels are secured and the data is thus transferred can be known by observing the brightness of the visible light, but a data transfer speed or a channel alignment state cannot be known; as a result, whether or not the data is transferred can be grasped by the brightness, thus the grasping is obscure.
Accordingly, the necessity of a new visible light communication technique is acutely on the rise, which allows the user to intuitively and clearly know the data transfer speed or the channel alignment state during communication using the visible light.